A stroke is a sudden loss of brain function caused by a blockage of a blood vessel to the brain (ischemic stroke) or a rupture of a blood vessel to the brain (hemorrhagic stroke). It is particularly desirable to detect stroke using an implantable medical device as many elderly patients prone to stroke already have such devices implanted therein or are candidates for such devices. Techniques for detecting stroke for use with implantable medical devices are described in published U.S. Patent Application No. 2010/0198082 of Park, entitled “Systems and Methods for use with an Implantable Medical Device for Detecting Stroke Based on Electrocardiac Signals” and in U.S. patent application Ser. No. 12/558,385 of Bharmi et al., filed Sep. 11, 2009, entitled “System and Method for use with an Implantable Medical Device for Detecting Stroke based on Physiological and Electrocardiac Indices.”
Cardiac ischemia is a condition whereby heart tissue does not receive adequate amounts of oxygen and is usually caused by a blockage of an artery leading to heart tissue. If sufficiently severe, cardiac ischemia results in an acute myocardial infarction (AMI), also referred to as a heart attack. With AMI, a substantial portion of heart muscle ceases to function because it no longer receives oxygen, usually due to significant blockage of the coronary artery. However, many episodes of cardiac ischemia are not sufficiently serious to cause actual permanent injury to the heart tissue. Nevertheless, it is desirable to detect such instances of “silent” cardiac ischemia. Note that cardiac ischemia is distinct from an ischemic stroke. Cardiac ischemia is an ischemia occurring within the heart that affects heart function. Ischemic stroke is an ischemia occurring within the brain that affects brain function.
Various techniques have been developed for analyzing morphological features of intracardiac electrogram (IEGM) signals sensed by implantable medical devices in an effort to detect cardiac ischemia. Some IEGM-based ischemia detection techniques seek to detect ischemia by identifying changes in the elevation of the ST interval of the IEGM that occur during cardiac ischemia. The ST interval represents the portion of the cardiac signal between ventricular depolarization (also referred to as an R-wave or QRS complex) and ventricular repolarization (also referred to as a T-wave). The elevation of the ST interval can increase or decrease due to cardiac ischemia or other factors.
Techniques for detecting cardiac ischemia using ST intervals or other features of the IEGM are discussed, for example, in U.S. Pat. No. 6,108,577 to Benser, entitled “Method and Apparatus for Detecting Changes in Electrocardiogram Signals” and U.S. patent application Ser. No. 11/394,724, of Ke et al., filed Mar. 31, 2006, entitled “Ischemia Detection using T-wave Amplitude, QTmax and ST Segment Elevation and Pattern Classification Techniques” and U.S. Pat. No. 7,225,015, entitled “System and Method for Detecting Cardiac Ischemia Based on T-Waves Using an Implantable Medical Device” to Min et al. See, also, U.S. Pat. No. 7,756,572 to Fard et al., entitled “System and Method for Efficiently Distinguishing among Cardiac Ischemia, Hypoglycemia and Hyperglycemia using an Implantable Medical Device and an External System.”
See, also, the following U.S. Patents assigned to Pacesetter, Inc., which discuss ischemia: U.S. Pat. No. 7,856,268, entitled “Ischemia Detection for Anti-Arrhythmia Therapy”; U.S. Pat. No. 7,792,572, entitled “Ischemia Detection using Intra-Cardiac Signals”; U.S. Pat. No. 7,756,572, entitled “System and Method for Efficiently Distinguishing Among Cardiac Ischemia, Hypoglycemia and Hyperglycemia using an Implantable Medical Device and an External System”; U.S. Pat. No. 7,648,464, entitled “Detecting Ischemia using an Implantable Cardiac Device based on Morphology of Cardiac Pressure Signal”; U.S. Pat. No. 7,610,086, entitled “System and Method for Detecting Cardiac Ischemia in Real-Time using a Pattern Classifier Implemented within an Implanted Medical Device”; U.S. Pat. No. 7,577,478, entitled “Ischemia Detection for Anti-Arrhythmia Therapy”; U.S. Pat. No. 7,502,644, entitled “System and Method for Distinguishing among Cardiac Ischemia, Hypoglycemia and Hyperglycemia using an Implantable Medical Device”; U.S. Pat. No. 7,460,900, entitled “Method and Apparatus for Detecting Ischemia using Changes in QRS Morphology”; U.S. Pat. No. 7,297,114, entitled “System and Method for Distinguishing among Cardiac Ischemia, Hypoglycemia and Hyperglycemia using an Implantable Medical Device”; U.S. Pat. No. 7,272,436, also entitled “System and Method for Distinguishing among Cardiac Ischemia, Hypoglycemia and Hyperglycemia using an Implantable Medical Device”; U.S. Pat. No. 7,769,436, entitled “System and Method for Adaptively Adjusting Cardiac Ischemia Detection Thresholds and other Detection Thresholds used by an Implantable Medical Device”; U.S. Pat. No. 7,524,287, entitled “System and Method for Distinguishing between Hypoglycemia and Hyperglycemia using an Implantable Medical Device”; U.S. Pat. No. 7,643,872, entitled “System and Method for Detecting Cardiac Ischemia based on T-Waves using an Implantable Medical Device”; U.S. Pat. No. 7,225,015, also entitled “System and Method for Detecting Cardiac Ischemia based on T-waves using an Implantable Medical Device”; U.S. Pat. No. 7,218,960, also entitled “System and Method for Detecting Cardiac Ischemia based on T-waves using an Implantable Medical Device” and U.S. Pat. No. 7,844,333, entitled “Pacing Therapy for Transient Ischemia Treatment.”
See, also, the following published U.S. Patent Applications: U.S. Patent Application 2011/0004111, entitled “Ischemia Detection Using Intra-Cardiac Signals;” U.S. Patent Application 2010/0081952, entitled “Detecting Ischemia Using An Implantable Cardiac Device Based On Morphology Of Cardiac Pressure Signal”; Patent Application 2009/0318987, entitled “Ischemia Detection For Anti-Arrhythmia Therapy”; Patent Application No. 2009/0177105, 2009/0177104, 2009/0177103, 2006/0167519, 2006/0167518, 2006/0167517 and 2006/0167365, each entitled “System and Method for Distinguishing Among Cardiac Ischemia, Hypoglycemia And Hyperglycemia using an Implantable Medical Device.” See, also, published U.S. Patent Applications: 2007/0016031 and 2004/0059220, both entitled “Systems and Methods for making Noninvasive Assessments of Cardiac Tissue and Parameters” and U.S. Patent Application 2007/0156056, entitled “System and Method for Detecting Cardiac Ischemia based on T-Waves using an Implantable Medical Device.”
Still further, see U.S. Pat. No. 5,113,869 to Nappholz; U.S. Pat. No. 5,135,004 to Adams et al.; U.S. Pat. No. 5,199,428 to Obel et al.; U.S. Pat. No. 5,203,326 to Collins; U.S. Pat. No. 5,313,953 to Yomtov et al; U.S. Pat. No. 6,501,983 to Natarajan, et al.; U.S. Pat. Nos. 6,016,443, 6,233,486, 6,256,538, and 6,264,606 to Ekwall; U.S. Pat. No. 6,021,350 to Mathson; U.S. Pat. Nos. 6,128,526, 6,115,628 and 6,381,493 to Stadler et al.; and U.S. Pat. Nos. 7,107,096, 6,985,771, 6,609,023, 6,468,263, 6,272,379, and 6,112,116, each to Fischell et al.
Hence, a variety of morphological features of electrocardiac signals can be used to detect cardiac ischemia. (Herein, electrocardiac signals generally pertain to cardiac electrical signals observed using any of a variety of sensing or detection techniques, including IEGM signals, surface electrocardiogram (EKG) signals or other suitable and appropriate signals, such as impedance signals.) Some of these parameters can also be affected by stroke. In this regard, disruptions in blood supply to the brain caused by stroke may lead to alterations of cardiac autonomic tone, such as increased sympathetic nerve activity. Thus stroke may lead to neurally mediated changes in electrophysiological properties of the heart that differ from those due to cardiac ischemia.
Accordingly, it is desirable to provide techniques for distinguishing stroke from cardiac ischemia. One such technique based on an analysis of electrocardiac signals and hemodynamic parameters is described in U.S. patent application Ser. No. 12/722,206 of Park, filed Mar. 11, 2010, entitled “Systems and Methods for use by an Implantable Medical Device for Detecting and Discriminating Stroke and Cardiac Ischemia using Electrocardiac Signals and Hemodynamic Parameters.” Briefly, techniques are described therein where a preliminary indication of stroke is detected based on an analysis of certain features of the IEGM, such as the onset of prominent U-waves, the onset of notched T-waves, and changes in ST segment duration or QT duration. Upon detection of a possible stroke, the device then detects one or more hemodynamic parameters that are typically affected by cardiac ischemia, such as cardiac contractility or stroke volume. The device then distinguishes stroke and cardiac ischemia from one another based on whether any changes detected in the hemodynamic parameters are consistent with cardiac ischemia.
It would be desirable to develop additional or alternative techniques for distinguishing stroke from cardiac ischemia and it is to these ends that the invention is generally directed.